Acupuncture has been used for centuries for pain relief in traditional Chinese medicine. In recent years, it has also been used for anesthesia in surgery. However, the basic rationale is not clear and has been rather difficult to investigate. The most plausible working hypothesis is that acupuncture is essentially operating through the CNS, resulting in an interaction of different sensory inputs from the point of acupuncture and from the site of pain. It is proposed to initiate laboratory research involving extracellular recording of single neuronal activity during concurrently administered acupuncture and noxious stimulation in the unanesthetized monkey. A microelectrode will be implanted surgically in the nucleus parafascicuris or nucleus centralis lateralis of a monkey which will be trained to sit in a restraining primate chair during experimental manipulations and to press a lever when noxious stimulus is given at irregular intervals. Pressing the lever would cut off the noxious stimulus immediately. Once trained, acupuncture procedures will be applied to an attempt to block the painful stimulus. Successful acupuncture will be defined in terms of the number of nerve stimulation administered to the monkey at noxious thresholds which are not followed by lever pressing. In other words, a decrease frequency of lever pressing following acupuncture is indicative of its analgesic effectiveness. These observations will be correlated with the recorded unit spikes of the thalamic neurons, and other behaviors indicating the presence or absence of pain.